What is Komatsu PC130-7 Fault Code S-6?

Komatsu PC130-7 Fault Code S-6 indicates a malfunction in the hydraulic oil temperature sensor circuit or an abnormal temperature reading in the hydraulic system. This code is triggered when the Electronic Control Module (ECM) detects that the hydraulic oil temperature sensor is sending values outside the normal operating parameters, or when there's a circuit fault preventing proper communication.

The hydraulic oil temperature sensor is critical for protecting the PC130-7's hydraulic system from overheating damage. The ECM uses this sensor data to adjust pump output, trigger warning systems, and prevent catastrophic hydraulic component failure. In older excavators, this system becomes especially vulnerable to sensor degradation, wiring harness damage, and connector corrosion—all of which can falsely trigger S-6 codes even when actual oil temperatures are normal.

Common Symptoms

When fault code S-6 is active on your Komatsu PC130-7, operators typically experience:

• Hydraulic overheat warning light illuminated on the instrument panel, even during cold startups or normal operating conditions
• Reduced hydraulic performance or derated machine functions as the ECM enters protective mode
• Intermittent code appearance that may come and go with machine vibration or temperature changes
• Abnormal temperature gauge readings showing excessively high or implausibly low hydraulic oil temperatures
• Machine hesitation during high-demand operations like digging or lifting heavy loads

Potential Causes

The most common technical reasons for S-6 fault codes on used PC130-7 excavators include:

• Failed hydraulic oil temperature sensor (internal resistance drift common after 5,000+ operating hours)
• Damaged or corroded sensor connector near the hydraulic tank mounting area where moisture accumulates
• Frayed or shorted sensor wiring harness, particularly at known rub points along the main boom swivel area
• Poor ground connection at the sensor mounting location due to rust or paint buildup on older machines
• ECM internal circuit failure (less common, but possible in high-hour machines with electrical system stress)
• Contaminated hydraulic oil causing actual overheating that triggers legitimate temperature warnings

How to Troubleshoot and Fix Code S-6

Step 1: Initial Visual Inspection Begin by locating the hydraulic oil temperature sensor mounted on or near the hydraulic tank. On used PC130-7 excavators, inspect the sensor connector for corrosion, oil contamination, or bent pins. Check the wiring harness from the sensor to the main harness bundle for visible damage, particularly where it routes near moving components or sharp edges.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor connector and measure the sensor's resistance at various temperatures. A properly functioning sensor typically reads 2,000-3,000 ohms at room temperature (consult your service manual for exact specifications). Check for voltage supply at the ECM side of the connector—you should see approximately 5 volts reference voltage. Test circuit continuity and ensure ground integrity at the sensor mounting point.

Step 3: Hydraulic System Verification Before replacing components, verify actual hydraulic oil temperature using an infrared thermometer on the hydraulic tank. Compare this to gauge readings. If temperatures are genuinely elevated (above 80°C/176°F), investigate cooling system problems like clogged hydraulic oil coolers, low coolant levels, or malfunctioning cooling fans—common issues in used equipment.

Step 4: Component Replacement and Clearing If testing confirms sensor failure, replace with a genuine Komatsu temperature sensor (avoid aftermarket sensors that may have incorrect resistance curves). Clean all connector contacts with electrical contact cleaner and apply dielectric grease before reconnection. After repairs, clear the fault code using Komatsu diagnostic software or a compatible diagnostic tool, then operate the machine through several heat cycles to verify the fix.

Used Excavator Consideration: On machines with 3,000+ hours, always inspect harness routing and secure any loose wiring that may have shifted over time. Replace any heat-damaged wire sections near the exhaust manifold area.

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Disclaimer: This guide provides general troubleshooting information. Complex electrical diagnostics and repairs should be performed by qualified technicians with appropriate Komatsu diagnostic equipment. Always consult your machine's service manual and follow proper safety procedures when working on heavy equipment.